1. Field of the Invention
The present invention relates to a thickness reducing management system for pipes in pipe lines which performs a thickness management for the pipes in pipe lines in plants such as an electric power generation plant and chemical plant which are controlled under demineralized water.
2. Conventional Art
Inside pipe lines of an electric power generation plant, steam of high temperature, high pressure and high speed, water of high temperature, high pressure and high speed and two phase fluid of steam and water of high temperature, high pressure and high speed flow, and the pipes in pipe lines are always subjected to a severe environmental circumstance. For this reason, such as erosion and corrosion are induced on the inside surfaces of the pipes in pipe lines and a secular thickness reducing phenomenon is caused thereon. When this thickness reducing phenomenon advances, there arises a danger of leaking the fluid inside the pipe lines which causes a significant problem. The speed of such thickness reducing phenomenon is not uniform with regard to space and time, and further it is understood that the thickness reducing speed also varies depending on a variety of conditions such as, for example, conditions of fluid in the pipe lines and configurations of the pipe lines. Therefore, a variety of experiments with regard to thickness reducing management for pipes in pipe lines were performed until now. Examples of such thickness reducing management systems for pipes in pipe lines in a plant are disclosed in following Japanese patent application laid open prints.
In a method of thickness reduction calculation and evaluation for machines and apparatuses, pipe line arrangement and the like due to erosion and corrosion as disclosed in JP-A-8-178172 (1996), a relationship between such as pipe material components, water quality and fluid flow speed representing parameters of erosion and corrosion inducing the thickness reducing phenomenon and thickness reducing data is analyzed based on thickness reducing measurement data base of more than one type plants and thickness reducing data base from documents data and experimental data which represent general data relating to thickness reducing speed, a mathematical model formula used for the thickness reducing calculation is prepared, in that a relationship between the parameters of erosion and corrosion and the thickness reducing amount is expressed by a function, data base for thickness reducing calculation formula due to erosion and corrosion is newly constructed for every condition of respective erosion and corrosion parameters, thereby, a thickness reducing calculation and evaluation thereof due to erosion and corrosion are realized based on the newly constructed thickness reducing calculation formula.
Further, thickness reducing managing system for pipes in pipe lines as disclosed in JP-A-10-141600 (1998) is for performing a thickness reducing management based on thickness values of the pipes in pipe lines. The thickness reducing managing system is provided with a recording means which records thickness values at a plurality of measurement points determined for every measurement portion; a thickness reducing speed calculating means which calculates thickness reducing speeds at the respective measurement points based on differences between thickness values at the present inspection of the respective measurement points and thickness values at the previous inspection of the respective corresponding measurement points and a plant operation time from the previous inspection to the present inspection; and a remaining life estimating means for estimating remaining life of the pipe lines for every measurement portion based on a maximum value among respective thickness reducing speeds at respective measurement points calculated at the present inspection and a minimum thickness value among respective thickness values for the respective measurement points.
In the thickness reducing calculation and evaluation method due to erosion and corrosion of the machines and apparatuses, pipe line arrangement and the like as disclosed in JP-A-8-178172 (1996), the pipe thickness reducing speed due to erosion and corrosion is expressed with regard many parameters such as temperature effect parameter, fluid flow speed parameter, dissolved oxygen density effect parameter, configuration effect parameter, pH effect parameter, pipe material component parameter and wetness degree effect parameter, however, it is difficult to determine that all of these parameters affect the pipe thickness reducing speed, therefore, the pipe thickness reducing speed calculation formula is not expressed with proper parameters. Further, even if the pipe thickness reducing speed can be calculated properly with the calculation formula, it is impossible to evaluate an inspection interval for the pipe lines based on the pipe thickness reduced amount.
Further, since the thickness reducing managing system for pipes in pipe lines as disclosed in JP-A-10-141600 (1998) performs the pipe thickness reducing management based on the thickness values of the pipes in pipe lines, only the data of a concerned measurement portion including a plurality of measurement points not of the other measurement portions in the pipe lines are used for the calculation of pipe thickness reducing speed and the evaluation thereof, therefore, it was difficult to analyze causes of the thickness reducing of pipes in the pipe line concerned. Further, even when a rapid pipe thickness reducing speed is measured for another pipe line under same condition of water quality and internal fluid state, the data of such rapid pipe thickness reducing speed can not be reflected on the thickness reducing management for the pipes in the pipe line concerned.
In the conventional method, too many parameters which affect the pipe thickness reducing due to erosion and corrosion are used, and in view of the pipe material components and the fluid state in the pipe lines it was difficult to define a proper pipe thickness reducing estimation formula which takes into account its causes, and a thickness reducing management of pipes in pipe lines which takes into account of safety of a plant was impossible.
An object of the present invention is to resolve the conventional problems as referred to above.
More specifically, an object of the present invention is to provide a thickness reducing management system for pipes in pipe lines in which a thickness reducing speed in the pipes due to erosion and corrosion is properly evaluated based on past and present data and through selection of limited proper parameters affecting thereto, thereby, reliability of remaining life evaluation of the pipes until the thickness thereof reaches to a minimum necessary thickness is enhanced and the pipe thickness reducing condition is correctly evaluated.
Further, an object of the present invention is to provide a thickness reducing management system for pipes in pipe lines in which a proper inspection internal can be set for every measurement portion of the pipe lines depending on the pipe thickness reducing condition and in view of pipe thickness reducing conditions of other measurement portions, therefore, a systematic maintenance and preventive maintenance scheduled for respective pipe lines can be planned, maintenance cost and inspection cost for the plant are reduced and optimized, and safety with regard to leakage of fluid flowing through the pipe lines is enhanced to thereby greatly contribute to a stable electric power supply.
According to one aspect of the present invention proposes a thickness reducing evaluation system for pipes in pipe lines, in particular, for pipes in pipe lines made of either carbon steel or low alloy steel in a plant controlled under demineralized water, which comprises a pipe thickness measurement result data base unit which stores pipe thickness measurement results for respective measurement points performed during inspection of the pipe lines; a point pipe thickness reducing speed calculation unit which calculates a measurement pipe thickness reducing speed through comparison of thickness measurement results at present inspection with thickness measurement results of the pipes in the pipe lines performed at the previous inspection both of which are stored in the pipe thickness measurement result data base unit; a pipe line condition measurement unit which is constituted by a first measurement subunit for measuring pipe line temperature or fluid temperature inside the pipe lines, a second measurement subunit for measuring wetness of the fluid in the pipe lines and a third measurement subunit for measuring fluid speed in the pipe lines; a pipe line condition data base unit which stores pipe line condition data from the pipe line condition measurement unit; a pipe thickness reducing speed model formula constructing unit which constructs a mathematical formula expressing pipe thickness reducing speed using the measurement result of pipe line temperature or the measurement result of the fluid temperature inside the pipe line, the measurement result of wetness of the fluid in the pipe lines and the measurement result of the fluid flow speed in the pipe lines as parameters and by making use of maximum values of the measurement pipe thickness reducing speed calculated by the point pipe thickness reducing speed calculation unit; a maximum pipe thickness reducing speed calculation unit which calculates a maximum pipe thickness reducing speed by making use of pipe line conditions at respective pipe thickness reducing measurement points concerned in the pipe lines; a next inspection interval calculation unit which determines an inspection interval until next time for the pipe lines through calculation of an interval when the pipe thickness of the pipe lines reaches a predetermined pipe thickness to be inspected by making use of the maximum pipe thickness reducing speed from the maximum pipe thickness reducing speed calculation unit and the predetermined pipe thickness to be inspected; and a pipe thickness measurement annual plan and schedule preparing unit which prepares a pipe thickness measurement annual plan and schedule based on the inspection interval until the next time inspection.
The above thickness reducing evaluation system for pipes in pipe lines can be modified in such a manner that the pipe thickness reducing speed model formula construction unit constructs the mathematical formula expressing the pipe thickness reducing speed by using pipe line temperature or fluid temperature in the pipe lines, fluid wetness in the pipe lines and fluid speed in the pipe line at the time of design stage thereof as parameters and by making use of the maximum values of the pipe thickness reducing speed calculated by the point pipe thickness reducing speed calculation unit, thereby, a simple pipe thickness reducing speed model formula can be constructed.
Further, in the above pipe thickness reducing speed model formula constructing unit and the above modified pipe thickness reducing speed model formula constructing unit, the total measurement data in the plant concerned are classified into three types, in that into the measurement data in the case where the inner fluid is a single liquid phase and the pipe material is carbon steel, the measurement data in the case where the inner fluid is two phases of gas and liquid and the pipe material is a carbon steel, and the measurement data in the case where the pipe material is a low alloy steel, for determining the pipe thickness reducing speed used for constructing the pipe thickness reducing speed model formula, and the thickness reducing speed model formula is constructed by making use of the thus classified total measurement data under respective conditions.
Further, in the above pipe thickness reducing speed model formula constructing unit, the pipe thickness reducing speed model formulas under the respective conditions are constructed in such a manner that in the case where the inner fluid is a single phase of liquid and the pipe material is a carbon steel, the measurement result of the pipe line temperature or the measurement result of the fluid temperature in the pipe lines and the measurement result of the fluid flow speed in the pipe line are used as the parameters for expressing the pipe thickness reducing speed, in the case where the inner fluid is two phases of gas and liquid and the pipe material is a carbon steel, the measurement result of the pipe line temperature or the measurement result of the fluid temperature in the pipe lines and the measurement result of the wetness of the fluid in the pipe lines are used as the parameters for expressing the pipe thickness reducing speed and in the case where the pipe material is a low alloy steel, the measurement result of the pipe line temperature or the measurement result of the fluid temperature inside the pipe lines is used as the parameter for expressing the pipe thickness reducing speed.
Further, in the above modified pipe thickness reducing speed model formula constructing unit, the pipe thickness reducing speed model formulas under the respective conditions are constructed in such a manner that in the case where the inner fluid is a single phase of liquid and the pipe material is a carbon steel, the pipe line temperature and the fluid flow speed in the pipe line which were estimated in the design stage thereof are used as the parameters for expressing the pipe thickness reducing speed, in the case where the inner fluid is two phases of gas and liquid and the pipe material is a carbon steel, the pipe line temperature and the wetness of the fluid in the pipe lines which were estimated in the design stage thereof are used as the parameters for expressing the pipe thickness reducing speed and in the case where the pipe material is a low alloy steel, the pipe line temperature which was estimated in the design stage thereof is used as the parameter for expressing the pipe thickness reducing speed.
Still further, the first subunit for measuring the pipe line temperature or the fluid temperature inside the pipe line constituting the above pipe line condition measurement unit evaluates the temperature of the inner surface of the pipe lines from the temperature of the outer surface of the pipe lines through a thermo couple attached on the outer surface of the pipe lines and a reverse problem analysis program based on thermal conduction analysis result thereof.
Still further, in the above next inspection interval calculation unit the next inspection interval is set in such a manner that a permissible pipe thickness reducing amount permitted until the next inspection which is obtained by subtracting the predetermined pipe thickness to be inspected from the present pipe thickness concerned is at first divided by the maximum pipe thickness reducing speed calculated by the above maximum pipe thickness reducing speed calculation unit and then the calculated interval is further divided by a predetermined safety rate.
Still further, in the above pipe thickness measurement annual plan and schedule preparing unit, the pipe thickness measurement annual plan and schedule is prepared in such a manner that the next inspection interval calculated by the next inspection interval calculation unit and the remaining life calculated by the remaining life evaluation and calculation unit are displayed with regard to all pipe line portions in the plant requiring inspection and further the inspection time after the next inspection is also displayed with regard to the all pipe line portions.